Every four years, about 100,000 Maine voters disappear.

It’s no magic trick: Almost everyone who can turns up at the polls to vote for president, but in the so-called midterm years – when we elect a governor – people just vanish.

That’s like the entire populations of Portland and South Portland slipping into the Bermuda Triangle. And when you count votes, it’s more than twice the margin of victory for a typical gubernatorial election, never mind the close ones.

But it’s not just the overall number that changes, it’s the composition of the electorate as well. Low-turnout midterms, like 2010 and 2014, have been reliably good for Republicans. High-turnout presidential years, like 2012 and 2016, have been better for Democrats and progressive causes.

The big question for 2018 is whether all those voters will disappear again, letting older, more conservative voters pick the next governor and Legislature. Or has everything that’s happened since Donald Trump’s election in 2016 changed the calculations?

A report earlier this year from the Voter Participation Center gave some good news to both sides. The organization gathers and publishes data on what it calls the “Rising American Electorate,” defined as unmarried women, minorities and young people (ages 18 to 34), who together make up nearly 60 percent of eligible voters.

Collectively, the groups are growing as a share of population, even in Maine, one of the oldest and whitest states. This demographic cohort cast 81,000 more votes in Maine’s 2016 election than it cast in the previous presidential year, 2012. That’s more than the margin of victory in the state’s presidential race, or either of the two (not very close) congressional races.

These are the fastest-growing demographic groups in the country, and while they are not exactly a monolithic bloc, they do share characteristics that suggest policy preferences.

Members of the “rising electorate” earn less than people in the other demographics. They are less likely to own homes and to have a college education, employer-provided health insurance or a pension.

They generally support policies like a higher minimum wage, paid sick days and universal health care. When they vote, they tend to vote for Democrats.

But they don’t always vote, and that’s the good news for Republicans in this report. The Voter Participation Project is projecting another major drop-off in this midterm election, and it predicts that the missing votes will come disproportionately from the group it tracks.

It estimates that even though they make up more than half of the population of eligible voters, 24 million fewer members of the “rising electorate” will vote in November than voted in 2016, as compared to 14 million fewer votes in all other demographics.

In Maine the researchers predict 156,000 fewer votes this year than were cast in 2016, with 88,000 of the missing ballots coming from the “rising electorate.”

So, armchair campaign strategists, how do you want to handle this? Do you want to assume that the historical pattern holds and the cohort of unmarried women, minorities and millennials turns out only in presidential years?

Or do you bet that the state is changing and this year will be different?

It’s easy to see what the Republicans plan on doing. All four gubernatorial candidates are firmly against expanding eligibility for Medicaid (known here as MaineCare), thus denying coverage to lower-income working people.

Republicans in the State House have tried to roll back the minimum wage and continue to promote cutting the top income tax rate as the key to economic development.

As you might expect, Democrats are also appealing to their base in the primary, but whoever emerges will be pressured to move to the center for November.

That might have been the right recipe in the past, but it doesn’t feel right for 2018. Certainly not if your success depends on bringing back the disappearing voters.

If Democrats want to win back the working class, they have to know that the working class has changed. It’s not just the guys you show up to shake hands with at the plant-gate photo-op. These days it’s also women who piece together a living from multiple service jobs. For the most part, they don’t get information about candidates from unions and they are too busy to follow politics. They need very good reasons that are very well articulated to show up at the polls.

Yogi Berra was once asked by a reporter if he was concerned about lagging attendance at his team’s games. He said it was out of his control:

“If people don’t want to come to the ballpark, how are you going to stop them?”

If Democrats are going to change the balance in Augusta, they are going to have to find a way.

Greg Kesich is the editorial page editor. He can be contacted at:

gkesich@pressherald.com

Twitter: gregkesich